There is a need in many industries to economically recover valuable products from what are considered to be wastes having a high moisture content and a non-uniform particle size. It is desirable to recover valuable products with greatly reduced moisture content, substantially uniform size, and without significant loss of beneficial attributes of the material. These industries include the agricultural, food processing, mining, coal, pulp and paper, and oil and gas industries. As one example, in livestock feed lots raw manure is produced in large volumes, and the most common reutilization mechanism is to apply it to land in the same water shed. However, such operations have become an environmental concern for a number of reasons, and in view of the large volume of manure produced (e.g. estimated to be about 1.4 billion tons of manure in the U.S.A. alone in 1998), stockpiles of manure and other waste products are becoming a significant cause for concern.
While presently a cause for concern, raw manure, when properly processed, has many applications. It can be used as a fertilizer, a soil amendment for such areas as parks, golf courses, and lawns, and in a number of other situations. In known systems, raw manure is typically mechanically milled or ground with hammer mills or grinders prior to processes in which the manure is dried in a rotary drum drier at between 350-500xc2x0 F. using an external heat source. A roll compactor is then used to form briquettes from the pulverized and dried raw manure, which are then re-ground to a desired granule size. Such systems have a number of environmental and economic drawbacks that make them largely, or wholly, not, cost effective.
Not only is conventional processing marginally or not cost effective, it also significantly reduces the quality of the processed product. The heat used for drying not only is produced expensively and with environmental adverse consequences, but it destroys a significant amount of the organic material in the manure. Also, the forming process produces a greater volume of airborne products that can present a health and safety hazard, requiring the utilization of air pollution controls.
According to the present invention, a method and apparatus are provided that overcome the drawbacks associated with the reduction of a large variety of different types of malleable material (such as manure, municipal sludge, coal and coal fines, food wastes, pulp and paper wastes, mine tailings, and dredge spoils). The method and system according to the present invention avoid almost all of the problems associated with the prior art systems and methods. According to the present invention one can produce a product having a much lower moisture content (typically a quarter or less of the original moisture content) while significantly reducing the average particle size (e.g. by at least 20%), and making the particle size substantially more uniform. The method of the invention can be practiced without any, or much less, external heat, and the organic content of the product produced is almost high as the initial organic content, typically not being reduced by more than about 15%.
According to one aspect of the present invention there is provided a method of drying and size-reducing malleable material, comprising substantially sequentially and continuously: (a) Feeding the material with a first moisture content and first average particle size into an air stream, to entrain the material in the air stream. (b) Increasing the speed of the air flow with entrained particles so that the speed is super-cyclonic and at least some of the particles are at super-cyclonic speed. (c) Causing the material to reduce in particle size by material to material collisions. (d) Reducing the speed of the air flow with entrained material particles so that substantially the entire flow is below super-cyclonic speed. And (e) separating the material, having a second moisture content at least 20% less than the first moisture content, and a second average particle size less than the first size, from the air flow.
Preferably (a)-(e) are practiced without the use of any external heat source, and (e) takes place by cyclonic separation. The method may further comprise wet scrubbing the air flow from (e), and under some circumstances after wet scrubbing, or other treatment, at least half of the air flow discharged from (e) may ultimately be recirculated. Also, in the practice of the method, (c) is practiced in at least two different stages, with the second stage inlet located vertically higher than the first stage. Also, preferably the cyclonic separation inlet in (e) is at a location vertically above the second stage of (c).
In the typical practice of the present invention, (b) is practiced to produce a substantially bullet profile of air flow with entrained material, having a substantially zero velocity at the periphery of the air flow, and a velocity of over about 400 mph at the center of the air flow; and (b) is typically further practiced so that the air flow speed approximately mid way between the periphery and center is about 225-275 mph. The air flow may be a first air flow, and (b) may be practiced by causing the first air flow with entrained material to pass through a truncated cone so as to gradually reduce the cross-sectional area of the first air flow by at least 10%, and by introducing a second air flow surrounding the reduced cross-sectional area first air flow.
In the further implementation of the invention, typically (a)-(e) are practiced so that the second moisture content is less than about one quarter the first moisture content, and so that the second particle size is more uniform than the first particle size. Also, typically (a)-(e) are practiced using an organic material having a final organic content in (e) not more than about 15% less than the initial organic material content in (a), and wherein (a)-(e) are further practiced so that the second moisture content is less than about one quarter the first moisture content. The method may be practiced using manure as the material, or alternatively municipal sludge, coal and coal fines, food wastes, pulp and paper mill wastes, mine tailings, dredge spoils, or various combinations thereof.
In the preferred practice of the invention, (c) is practiced in at least one cyclone-shaped vessel, and further comprises directing an auxiliary flow of air into the at least one cyclone-shaped vessel to adjust material retention time in the vessel. The method may further comprise causing the material entrained in air flow to be introduced tangentially into the at least one cyclone-shaped vessel, and to impact a plurality of breaker bars in the vessel to facilitate particle size reduction.
In another aspect of the present invention a material drying and particle size-reducing apparatus is provided comprising: A blower. An air lock feeder operatively connected to receive air from the blower and downstream thereof. An accelerator for increasing the speed of air flow from the blower, with entrained material from the air lock feeder. At least one particle size reducer operatively connected to the accelerator downstream thereof. And a separator for separating reduced average particle size and drier material from the air flow, the separator operatively connected to and downstream of the at least one particle size reducer.
Preferably the material comprises a housing having a first open end operatively connected to the air lock feeder, a second open end operatively connected to the at lest one particle size reducer; a central conduit having a first end at or adjacent the housing first end, having a first diameter, and a second open end within the housing having a second diameter at least 10% less (e.g. about 30-35% less) than the first diameter; and a truncated cone portion of the central conduit between the first and second diameter portions thereof. The accelerator may further comprise a substantially annular chamber surrounding the second end of the central conduit within the housing, and a connection to the blower in the annular chamber between the first and second ends of the central conduit and at least about six inches from the central conduit second end.
In the preferred embodiment, the at least one particle size reducer comprises at least first and second cyclone-shaped vessels connected in series, the first cyclone-shaped vessel between the second cyclone-shaped vessel and the accelerator; and wherein the vessels each have an inlet and an outlet; and wherein the second vessel inlet is vertically above the first vessel inlet and the first vessel outlet is connected by a curved conduit to the second vessel inlet. Preferably the separator comprises a cyclone-shaped separator vessel with a particle outlet at a bottom portion thereof and an inlet at a top portion thereof; and wherein the separator vessel inlet is vertically above the second particle size reducer vessel and connected thereto by a curved conduit.
Also, the separator may comprise first and second air outlets from a top portion of the separator vessel, above the separator vessel inlet. The first and second cyclone-shaped vessels may also include valved auxiliary air inlets at the bottom portions thereof, the auxiliary air inlets operatively connected to the blower and the valves being adjustable to control the auxiliary air flow to control the retention time of material particles in the vessels.
It is a primary object of the present invention to provide a simple, cost effective, and energy and environmentally sound method and apparatus for processing waste products so as to reduce the moisture content and average particle size thereof. This and other objects of the invention will become clear from an inspection of the detailed description of the invention and from the appended claims.